There is one implication. We must consider the fact that air box will be sealed right? I would personally leave a vent of somesort somewhere.
The reason for this is that, we must consider the internal dimensions of the cold air box, and its volumetric capacity. We must also consider the demand for air when the car is experiencing rather alot of thrape (as mine does regularly).
The demand for air will empty the air box within a millisecond and we must ensure that the ducting is of sufficient diameter and as unrestrictive as possible to enable that air box to be full all the time. Remember that without the airbox in place, the filter at the end of the induction tube has alot of area to draw air from. I would imagine that the spare space in that corner of the engine bay equates to about half a cubic meter with several areas where air can enter. An air box will be a fraction of this, with only one, possibly two intakes with a low internal diameter.
If the car is demanding more air than what is FREELY available, then it will create a partial vacuum inside the box and basically the intake ducting will become a vacuum cleaner and have to suck the air in from outside, which is making the engine work harder for its air, therefore POWER LOSS. If I can remember my physics, isnt this called volumetric efficiency, or something like that.. :duh:
I would personally place a vent toward the front of the air box, just to maximise air flow at high demand.
This is only some of my theory folks, dont take it as gospel. I wonder if Mark at TDi would agree/disagree with any of my theories, or anyone else come to think of it.